The growth of networking and the popularity of the Internet have created a need to improve the performance and reliability of network architectures. For example, FIG. 1 shows a block diagram of a local network 100 according to a conventional network architecture. Network 100 is connected to a network backbone 102 that connects several external networks. Backbone 102 may be, for example, the Internet or an Intranet. In this example, network 100 includes a router 104 connected to backbone 102 through a interface 105. Network 100 also includes a first server 106 connected to router 104 through a interface 107 and a second server 108 connected to router 104 through a interface 109. In this example, network 100 uses the TCP/IP communication protocols, which are well known in the art of networking.
Clients connected to backbone 102 may send packets to a specific server in network 100 (e.g., server 106) through router 104. Conversely, server 106 may send packets to the client through router 104 and onto backbone 102. However, network 100 is not fault tolerant in that router 104 represents a possible single point failure for network 100. More specifically, when router 104 fails, servers 106 and 108 can no longer communicate with clients connected to backbone 102. In particular, servers are typically not configured to detect failure of "first hop" routers (i.e., the first router encountered by an outbound packet from a server). Thus, the servers will continue to send packets to the failed router, never knowing that the outbound packets do not leave network 100 (sometimes referred to as a "black hole" for outbound traffic).
One conventional scheme to eliminate this single point failure is to include a second router in the local network. FIG. 2 shows a block diagram of a network 200 according to such a conventional scheme. In this example, network 200 includes a second router 202 connected to backbone 102 through an interface 203. Routers 202 and 104 are connected to a shared media 204 (e.g., Ethernet cable) through interfaces 206 and 208. Servers 106 and 108 are connected to shared media 204 through interfaces 210 and 212, respectively. Although the second router 202 does provide fault tolerance, the use of shared media 204 undesirably increases the complexity of network 200 and degrades the performance of network 200.
In one implementation of this conventional scheme, fault tolerance is mainly implemented on the servers. In particular, the servers are special servers configured to listen to the router information protocol (RIP) and can detect the failure of a router. Then these servers can adapt to reconfigure themselves to change the default router. However, this scheme places a large burden on the server to listen and process the complete routing table that exists in the network. Consequently, server performance is significantly impacted by this scheme, which, of course, is undesirable. Further, this processing of the RIP information takes on the order of several minutes, which is a relatively long time to correct a router failure. This relatively long correction time undesirably allows a significant number of packets to be sent to the "black hole."
In another scheme that is implemented in the routers as well as in the servers, servers 106 and 108 are configured with a "virtual" Internet protocol (IP) address different from the regular interferace IP addresses of routers 202 and 104. Routers 202 and 104 are configured with a virtual IP address and monitor every packet on shared media 204. Thus, when one router fails, the other router detects this failure and can then handle the packets of the failed router.
Although this virtual IP address scheme may represent an improvement in detection of a failed router over the previously described scheme, several problems remain. For example, this scheme is intrusive in that this scheme requires the use of special routers and specially configured servers that support this virtual address scheme. Thus, this scheme may not be practical for a user already having a significant investment in servers and routers that do not support these virtual address features. In addition, the presence of a third router IP address may confuse the network management system used by the user.